Research suggests that broad classes of psychopathology are organized along orthogonal dimensions termed internalizing and externalizing. Factor analytic work demonstrates that these temperament-based latent factors account for the expression, severity, and comorbidity in major mental disorders. Recent studies have extended this model into the realm of trauma, providing evidence that these dimensions may similarly account for patterns of comorbidity in posttraumatic stress disorder (PTSD). This work on the structure of PTSD comorbidity is limited to the study of comorbid Axis I disorders and by largely descriptive analyses. Therefore, the goal of the present cross-sectional study is to use multivariate analytic techniques to more fully examine the internalizing and externalizing structure of PTSD comorbidity in the Axis II domain and to investigate the temperament factors that predict the phenotypic expression of this comorbidity in a sample of 250 men and women with PTSD. Doing so will provide support for a parsimonious, dimensional conceptualization of PTSD comorbidity and extend theory on the structure of mental illness into the realms of trauma and Axis II psychopathology. [unreadable] [unreadable] [unreadable]